1. Field of the Invention
The present invention relates to a developer cartridge and an image forming apparatus using this cartridge, and, more particularly, to a developer cartridge for exchanging developers in a developing apparatus, and an image forming apparatus using this cartridge.
2. Description of the Related Art
In an image forming apparatus such as a copying machine, a printer or a facsimile, an electrostatic latent image is formed on a latent image carrier like a photosensitive drum. A developing apparatus is used to develop an electrostatic latent image with a developer. A typical developer used in the developing apparatus is composed of two components, toner and carrier. As the toner in this developer is consumed in a developing process, additional toner should be supplied. This requires that a toner cartridge in use be exchanged with a new one. Further, the developer in the developing apparatus deteriorates with the passage of time so that the quality of an image becomes lower. It is therefore necessary to exchange the old developer with a new one. Recently, those exchanges are often conducted by the user of the image forming apparatus. In this respect, there is a demand for an image forming apparatus designed to facilitate the developer exchange without making the operator's hands dirty.
In general, the developer exchange is conducted as follows. A developer cartridge containing an unused developer and an empty collecting cartridge for collecting the developer in the developing apparatus are placed in the developing apparatus. Then, after the developer in the developing apparatus is collected in the collecting cartridge, the unused developer is supplied into the developing apparatus from the developer cartridge. This method involves two cartridges, thus complicating the exchange.
For example, U.S. Pat. No. 5,109,254 and Japanese Unexamined Patent Publication No. 118675/1992 proposed a developer cartridge having those two cartridges designed as a single cartridge to ensure automatic exchange of developers. In the proposed method, a developer exchanging section is provided on a side of the developing apparatus. The developer cartridge comprises a cylindrical portion, a developer storage room which is located above the cylindrical portion and where a used developer is retained, and a collecting room located under the cylindrical portion. This developer cartridge is placed in the developer exchanging section of the developing apparatus. More specifically, the cylindrical portion of the developer cartridge is fitted in the developer exchanging section of the developing apparatus. When the shutter of the collecting room of the developer cartridge is open, the used developer in the developing apparatus falls into the collecting room from the developer exchanging section. Then, the shutter of the collecting room is closed and the shutter of the developer storage room is open. As a result, the unused developer in the developer storage room falls into the developer exchanging section to be supplied into the developing apparatus. The developer in the developing apparatus is exchanged with a used developer in this manner.
The aforementioned Japanese Unexamined Patent Publication No. 118675/1992 also discloses that a toner storage room for storing a supplemental toner is provided next to the developer storage room.
According to these exchanging methods, when the developer cartridge is set, a sequence for exchanging the developer cartridge is automatically executed. In the used cartridge, the developer storage room is empty while the collecting room is full of the waste developer. When such a used developer cartridge is erroneously set in the image forming apparatus, used developer in the developing apparatus falls into the collecting room-full of the waste developer, so that the developer will overflow from the collecting room, staining the apparatus.
The aforementioned U.S. Patent Publication discloses a developer cartridge provided with a fuse to overcome the above problem. In this method, when the developer cartridge is set in the image forming apparatus, a current path running through the fuse is formed to drive the motor or the like of the apparatus. This fuse is designed to be gone after a given time at which the developer exchanging sequence will be complete. Therefore, the fuse of the developer cartridge after exchange is gone, so that even when this cartridge is set in the apparatus, no current would flow through the driving circuit of the apparatus. Naturally, no exchanging sequence would be executed, thus overcoming the aforementioned shortcoming.
But this known technique of overcoming the problem requires that a fuse contact be provided on the apparatus side and the fuse of the developer cartridge surely be connected to that contact by manual setting of the developer cartridge. The fuse of the developer cartridge is likely not to have an electrical contact with the contact of the apparatus, so that the exchanging sequence even for a new developer cartridge may not be executed due to an electrical contact failure. With regard to the aforementioned developer cartridge further provided with the toner storage room, the time for the toner in the toner storage room to run out is not constant. With the aforementioned fuse utilizing technique, the drive current may be cut off after the exchanging sequence is accomplished, disabling the toner supply. Further, if the driving circuit of the apparatus fails, a large current will flow at the beginning of the exchanging sequence, thus blowing the fuse spontaneously. This undesirably sets a developer cartridge before exchange as an exchanged cartridge.
Furthermore, when there are a large amount of the developer to be exchanged and a large amount of the toner supplement, however, it is necessary to make the developer storage room, toner storage room and collecting room of the developer cartridge longer. In this case, the developer cartridge inevitably becomes larger in length. This makes the handling of the developer cartridge troublesome, and requires extra space for storage of such developer cartridges. It is also necessary to provide extra space for placing the developer cartridge in the relatively narrow space around the photosensitive drum, resulting in enlargement of the developing apparatus. In addition, the developer exchanging section of the developing apparatus should be made smaller due to the additional portion of the developing apparatus.. But it is troublesome to conduct the developer exchange in the small exchanging space. Furthermore, as a toner is supplemented using this small developer exchanging section, the amount of a supplementable toner is small so that the toner supplement may not be accomplished in time.